In the animal world, communication is one of the most vital aspects as it is unlikely that many species would survive or live long healthy lives without it. However, it can be challenging for creatures who live in the ocean. Underwater, light and odours do not travel well, making it difficult for marine animals to see or smell. But sound travels four to five times faster through water than through air, so in the marine ecosystem, mammals rely on creating sounds or vocalizations to communicate. That is why a variety of noises filled the ocean: clicks, chirps, whistles, moans, screams, clanks, cries, trills, and other intricate sounds. But the prominent part of this underwater symphony is the intense melody or song of one of the world’s largest mammals, the humpback whale. The song they create has a mysterious feel to it, but they are so pleased to hear.
Humpback is one of few species of baleen whales that are known to sing. Meanwhile toothed whales like orca, do use echolocation and make social sounds to communicate, but those vocalizations lack the complexity of songs. All humpback whales – males and females, can make social calls from an early age. Even neonate whales – those less than a month old – have been known to make vocalisations recognisable to the human ear. However, it is only the male humpback whales that truly sing. Their songs are the most complex, non-human, acoustic displays communication system in the animal kingdom. The song itself is continually evolving, continually changing through time – being passed from one population to the next. And all males are incorporating these changes into their own song as populations come into contact with each other. The best analogy now is human fashion, where a new pop song comes available, and everyone is suddenly listening to it.
As with many aspects of whale song, the biological systems humpbacks use to create their vocalizations are not completely understood yet. However, experts have established a theoretical understanding of how the songs are formed. Whales make sound by moving air between numerous sinus cavities in their skull and across something called ‘phonic lips’ or ‘vocal folds.’ In this sense, it is not that different from human. One of the huge distinctions between us and humpback whales is that when we make sound, air expels from our mouth – we are inhaling and exhaling as we do so. Whereas when humpback whales vocalize, they are doing so underwater in a closed system – they are moving air all around on the inside. The humpback whale has a U-shaped fold of tissue between the lungs and the laryngeal sac, a large inflatable organ. Researchers suspect that when humpback whales make sounds, muscle contractions in the throat and chest move water from the lungs through the U-folds into the laryngeal pouch, causing the U-folds to vibrate. The resulting sound resonates in a pocket like a cathedral choir making the sound loud enough to spread thousands of kilometers away. Whales do not have to exhale to make a sound. Instead, the air is exhaled back into the lungs, producing sound once more. The reason whale singing is so astonishing is because of the patterns. The units, such as moans, screams, and squeaks, are forming phrases. These phrases are repeated over and over to assemble into themes. Several themes are repeated in a certain pattern into a single song.
So why do humpback whales sing? What is the purpose of their song? At the moment, researchers have yet to form a complete understanding. They assessed that male humpback essentially sing to communicate with their male friends as part of male-male competition, or to mark territory, scaring off other male whales, or they could be a multi-message signal. Some say the male humpback whales sing to attract females as they sing most often during the breeding season, but it is not that simple. When researchers played whale songs around female humpback, it was actually the male that came. This communication is done for alliances in attracting the attention of females. This alliance is useful so that the whale is superior to its competitors. Another theory is that the male humpback whales sing together and form “bands” to attract females. When the whales perform together, the female whales just have to choose which male they are interested in. One innovating new research has observed how humpback whale’ songs have spread and evolved throughout the South Pacific. Their songs are constantly changing, units or phrases added or removed. Humpback whales return to their foraging and breeding grounds, every year, and each separate population has a different song. After considering several possible explanations, the researchers suggest that the difference between songs might be due to large-scale changes in the marine environment. When males from different populations forage within hearing distance, phrases are often exchanged. This is one of the fastest examples of cultural spread, where learned behaviour is transmitted between individuals of the same species. The observation shows an extensive, well established, acoustic community that may connect whales worldwide – and help them form life-long relationships.
Humpback whales have habitats in all over the oceans, so they can actually perform their songs across the world. Researchers have eavesdropped on those songs using an underwater microphone called a hydrophone. The tool helps to track species with rare sightings and genetics. For example, scientists have been able to distinguish populations of hard-to-find blue whales based on their singing. Whale songs vary widely in duration, and they are sung repeatedly. Sounds picked up by the hydrophone have been recorded almost continuously. In one recorded session, humpback whales sang for 22 hours. The recent paper shows that humpbacks in the Monterey Bay area mostly sing at night. In fact, during their peak singing season (November through January), humpbacks song was audible about 70 percent of the time during the night-time hours. They sang much less during the daytime, with the least amount of song (about 30 percent of the time) around noon. Humpback songs around Hawaii and off South America follow a similar daily pattern. The researchers speculate that the whales in Monterey Bay might focus on feeding during the daytime and thus have more time to sing at night.
But the ocean is getting noisy because of human activities. Boats, military sonar, underwater construction, and seismic research in search of oil are becoming increasingly common which can disrupt whale communications. Whales will avoid foraging and breeding grounds if the noise by humans is too loud. Blue whales have been observed to reduce their singing due to noise that is 200 kilometers away. Limiting human activity along migratory routes and in other important habitats and reducing noise pollution across the oceans will help ensure whale survival. Without communication it is unlikely that many species would survive or live long healthy lives. If whales can keep on singing and we can still hear them, maybe one day we can really understand what they are talking about. The only reason for that is to find out something that is critically important. After all, if we are going to protect this extraordinary animal from noise pollutions, we have to understand what these calls are for.